Alkylation is the reaction of adding an alkyl or an alkenyl group to a compound. Acylation is the reaction of adding an acyl group to a compound. Although alkylations are often referred to as acid-catalyzed Friedel-Crafts-type reactions, they can also refer to the preparation of alkylates in refinery conditions. These processes are useful for synthesizing fine chemicals for pharmaceutical and agricultural chemicals, as well as large volume chemicals. The large volume chemicals include: ethyl benzene from benzene and ethylene (in excess of about 23 million metric tons/year); cummene from benzene and propylene (in excess of about 9.5 million metric tons/year); bisphenol A from phenol and acetone (about 1.1 million metric tons/year); and alkylbenzenes from benzene and C10-C18 olefins to (about 900,000 metric tons/year). Other chemicals include: alkylbenzenes from propylenes, isobutene, butylenes and amylenes; detergent alkylates from benzene and linear aliphatic olefins; xylene; polynuclear aromatics alkylated with olefins and olefin-producing reagents; alkylated phenol derivatives (2,6-xylenol, o-cresol); alkylated aromatic amines (e.g., 5-tert-butyl-2,4-toluenediamine); and alkylated pyridines.
A problem with many of these processes is that selectivity to the desired product is often less than desired. As a result, costly downstream purification procedures are often required. For example, in the production of ethyl benzene from ethylene and benzene, undesired by-products such as polyethyl benzenes, xylene, C3+ alkenes and other undesirable by-products are typically produced.